Thousands of students on Friday walked out of their high schools, some for a good part of the day, in a second nationwide protest of gun violence since the February mass shooting at a school in Florida that left 17 people dead.

Friday’s event was tied to the 19th anniversary of the Columbine High School massacre in Colorado, which killed 13. Since the shooting two months ago at Marjory Stoneman Douglas High School in Parkland, Fla., students from that school have kicked off a nationwide movement to advocate tighter gun laws.